#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdbool.h>
struct ListNode 
{    
    int val;
    struct ListNode* next;  
};

bool hasCycle(struct ListNode* head) {
    struct ListNode* fast = head;
    struct ListNode* slow = head;
    while (fast && fast->next)
    {
        slow = slow->next;
        fast = fast->next->next;
        if (slow == fast)
        {
            return true;
        }
    }
    return false;
}